Internal electronic components, used for manufacturing an organic or inorganic light emitting device, a display device, a solar cell device or the like, have to be protected from environmental chemicals such as oxygen and moisture. Conventionally, glass plates are used as a substrate or cover sheet to protect the internal electronic components which are susceptible to the chemicals. The glass plates are advantageous in that they exhibit satisfactory characteristics in light transmittance, thermal expansion coefficient, and chemical resistance. However, since they tend to break easily, be heavy and hard, there are some limitations in terms of ease of handling and design.
Recently, there are many studies to replace the glass plate used as a substrate for such electronic devices with plastic counterparts, since the plastic substrate is advantageous over the glass plate in terms of weight, impact-resistant and flexibility. Unfortunately, since commercially available plastic films have many drawbacks, compared with the glass plate, improvements in physical properties, in particular, gas barrier property, are necessary.
When an inorganic material that is metal oxides or nitrides is layered on a plastic substrate in order to produce a multiple film, it is known that the gas barrier property of the multiple film increases as the thickness of the inorganic layer is increased. However, if the thickness thereof is increased to a certain level or more, which depends on the kind of the inorganic material that is used or the film formation condition, it is known that further increase in the gas barrier property is insignificant (Thin Solid Films 388 (2001) 78; Vacuum 68 (2003) 113). This level-off behavior comes from defects present in the inorganic layer, and in order to overcome the above limit and increase the gas barrier property, in the related art, there is an example of a specially designed structure in which organic and inorganic layers are repeatedly stacked several times (Barix™ film structure manufactured by Vitex, Co., Ltd.). However, in the multiple film of the repeatedly stacked structure, there are a number of interfaces of the organic and inorganic layers having different surface characteristics and, therefore, the adhesion failure between the layers can easily occur.
Meanwhile, gas barrier films are produced by depositing inorganic materials of metal oxides or nitrides including SiOx, AlOy, SiOaNb, AlOcNd, ITO and the like, which have the excellent gas barrier property, on plastic films having flexibility, but the inorganic material layers that are formed by the above art are susceptible to moisture and the gas transmission rate increases under humidity (Surf. Coat. Tech., 74/75 (1995) 676; Surf. Coat. Tech., 142/144 (2001) 163).
In addition, the gas barrier film has a disadvantage in that the moisture transmittance continuously increases with time. This is the result of degradation of the inorganic material layer due to moisture. Accordingly, it is necessary to prevent degradation of the inorganic material layer under humidity by putting a protective layer that has water resistance or the water repellent property on the inorganic material layer.
Meanwhile, it is known that metal aluminum is better than aluminum oxides in terms of the moisture barrier performance (Thin Solid Films, 355/356 (1999) 500), and among the deposition modes for metal oxides, that is, the oxide and metal modes, the metal mode gives a deposition layer with a better moisture barrier property (J. Electrochem. Soc., 149 (2002) B 487).
Korean Patent Registration No. 10-0575563 discloses a structure in which a metal oxide and a metal (for example, Ag) are layered in contact with each other. The metal layer is excellent in moisture barrier performance but the light transmittance is largely reduced (J. Appl. Phys., 47 (1976) 4968) and, therefore, in the above patent, a method for maintaining the light transmittance by additionally putting the reflection prevention layer is suggested. In this case, in order to obtain the excellent light transmittance, it is necessary to precisely control the refractive index and the thickness of the reflection prevention layer that is the additionally layered.